This invention relates to a method of setting up apparatus for handling electrical or electronic components, for example in a component placement machine. The components may be of a variety of shapes and sizes, for example so-called flat packs, S.O style transistors, leadless chip carriers, dual in line packages, melf type components and the like, as well as so-called "chips" .
In the manufacture of electrical or electronic apparatus it is necessary to assemble a plurality of components on a suitable substrate, for example a printed circuit board. A number of systems have been proposed for handling the components to be placed on a substrate and many of these have proposed the use of pick-up heads having a suitable tool by which a component may be picked up. The tools have been of various types, depending to some extent on the components to be handled; for example the tools may grip the components mechanically or may use suction or a magnetic system to retain a component on the tool of the pick-up head when the component is removed from a suitable component supply means for delivery elsewhere, for example to a suitable placement position where the component may be placed on a substrate e.g. a printed circuit board. It is important to ensure that the components are correctly oriented when placed on the substrate and a number of methods have been proposed to attempt to ensure correct orientation.
In component placement machines of the type described, the substrate, for example a printed circuit board, on which the components are to be placed, is mounted in an accurately known position on an X-Y table, suitably mounted on a frame. The X-Y table may be mounted and driven by any suitable means, a number of which are known, and one such means for mounting and driving an X-Y table is described by way of example in our PCT Patent Application Publication No. W.O. 85/03404.
Whilst the movement of the X-Y table can in theory be determined accurately an precisely by control of its drive mechanism, there can in practice be some deviation between the theoretical and the actual response of the table to the drive mechanism. This can result in a deviation from the intended location of the X-Y table, and hence the substrate mounted on it, which can lead to inaccurate placement of a component on the substrate.
Clearly if this inaccuracy in placement of the component exceeds any permissible tolerance, then an unacceptably high reject rate for the completed substrates will result.
An improved method of setting up a component placement machine in which any inaccuracy in the positioning of a point on a substrate mounted on the X-Y table relative to a reference point, which inaccuracy is due to the response of the X-Y table to its drive system, is reduced or substantially obviated, is described and claimed in our co-pending U.S. patent application Ser. No. 295,968 filed 1/11/89.
In our U.S. patent application Ser. Nos. 150,101, filed 1/29/89, 150,128 filed 1/29/88 and 149,799 filed 1/29/89, a component placement machine is described by way of example in which a plurality of pick-up heads each provided with a pick-up tool, are mounted on a support, and, in operation means are provided for moving the pick-up heads through a number of stations at which operations such as pick-up, inspection and placement may be carried out. In the inspection operation, the position of the component relative to the pick-up tool is detected and a correction is applied to the X-Y table drive for any deviation of the component from a reference position. The position of the component is detected by a CCD camera looking upwards at the component and the orientation of the component can also be detected and corrected by rotation of the tool about a vertical axis.
In such a component placement machine, in operation, the pick-up head has an up-position and a down-position, and can be moved between the up-position and the down-position. The pick-up head carries out its pick-up and placement operations while in the down-position but the inspection is carried out in the up-position. The placement is rendered less accurate by any movement in a horizontal plane of the pick-up tool in moving from its down-position to its up-position as such movement leads to the position of the component detected in the inspection operation, which includes this movement, not being an accurate reflection of the position of the component when placed. This movement may be different for each pick-up tool. Thus, this movement in a horizontal plane leads to placement inaccuracies.